Breast prostheses have been available to increase breast size (augmentation) and to restore the breast mound in reconstruction procedures following mastectomy. The prostheses typically have an outer shell or envelope of thin silicone elastomer and are either prefilld with a silicone elastomer "gel" or are filled with a saline solution through a tube and valve after implacement. The prostheses are available in numerous sizes (volumes), several shapes including tear drop, round, low-profile, etc. Some have Dacron patches on the back to allow fibrous tissue ingrowth causing the prosthesis to be adherent to the chest wall or pectoralis muscle. Usually prostheses are implanted via a small inframammary or peri-aerolar incision into a pocket dissected deep to the patient's own breast tissue in front of the pectoralis muscle. In certain circumstances, such as reconstruction after mastectomy, the prosthesis may be placed behind the pectoralis muscle.
In all cases, the prosthesis is surrounded by a natural "capsule" composed of fibrous scar tissue after it has been implanted for some period of time. This is a normal tissue reaction to the presence of a foreign body. Scar normally undergoes contracture during the healing process. This capsule of scar tissue contracts to variable degrees in all patients to deform the prosthesis toward a sperical shape to minimize the ratio of capsule surface area to volume of breast prosthesis. The contracture of the capsule may be slight so that the breast feels soft (i.e., natural) when examined or it may so compress the silicone elastomer gel or saline contents of the prosthesis that the breast will feel quite hard (i.e., unnatural) when examined. Where any given augmented breast falls on the spectrum from soft to hard depends upon the patient's own scar conracture process in trying to decrease the ratio of capsule surface area to volume of breast prosthesis. It has been reported that flexible silicone backings placed behind the soft front envelope result in a softer breast mount. However, since the backings were not rigid, they tended to curl up against the front envelope due to scar capsule contraction when placed in the usual location over the pectoralis muscle. Rybka and Cocke "The Value of Silicone Dacron-Felt Discs in Prevention of Capsular Contractions" Plastic Surgical Forum, Vol. 1, p. 221 (1978).
A basic requirement of any mammary prosthesis is that it can be inserted through a three to four centimeter incision. Hence, the backing cannot be rigid until implanted in a pocket behind the breast. Further the edges of the backing of the implant must not be palpable. A backing member must contour itself to the chest wall and/or the pectoralis muscle over which it is laid so that it does not rock back and forth. The prosthesis should not interfere with chest X-rays and mammography.
Two patents which relate to mammary prostheses are U.S. Pat. Nos. 3,293,663 and 3,934,274.